Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Vehicles can be configured to operate in an autonomous mode in which the vehicle navigates through an environment with little or no input from a driver. Such autonomous vehicles can include one or more sensors that are configured to detect information about the environment in which the vehicle operates. The vehicle and its associated computer-implemented controller use the detected information to navigate through the environment. For example, if the sensor(s) detect that the vehicle is approaching an obstacle, as determined by the computer-implemented controller, the controller adjusts the vehicle's directional controls to cause the vehicle to navigate around the obstacle.
One such sensor is a radio detection and ranging (RADAR) system. A RADAR system actively estimates distances to environmental features by emitting radio signals and detecting returning reflected signals. Distances to radio-reflective features can be determined according to the time delay between transmission and reception. The RADAR system can emit a signal that varies in frequency over time, such as a signal with a time-varying frequency ramp, and then relate the difference in frequency between the emitted signal and the reflected signal to a range estimate. Some systems may also estimate relative motion of reflective objects based on Doppler frequency shifts in the received reflected signals. Directional antennas can be used for the transmission and/or reception antennas to associate each range estimate with a bearing. Combining the measured distances and the directional information allows for the surrounding environment features to be mapped. The RADAR sensor can thus be used by the autonomous vehicle control system to avoid obstacles indicated by the sensor information.
Beamforming is the combination of signals from an array of spatially separated antenna elements to simulate signals from larger directional antenna. The simulated antenna beam/lobe, or directional sensitivity of the array, can be electronically steered by applying phase offsets to signals received from the individual antenna elements (or to subarrays of such elements). When suitably steered, signals received at each antenna element from the desired direction of the beam are coherently combined. Phase offsets can be applied by analog phase shifters that are electronically controlled or can be applied digitally once the received signals are converted to digital. Some beamforming techniques may also weight the amplitude of the signals received from each element to further tune the nulls and lobes of the received radiation pattern.